In order to keep gap losses affecting the efficiency of gas-turbine engines small, it may be necessary to keep the gap between the turbine blades rotating at high speed and the housing surrounding them small for as long as possible.
The gap dimension of this gap is known not to be constant, but is subject to changes during the different operating phases of the gas-turbine engine. Thus, among other things, the turbine blades experience elongation in the radial direction under high working loads, due to thermal stress and the acting centrifugal force. In addition, the housing surrounding the turbine blades has a different thermal reaction characteristic. All of this results in the gap-dimension changes to be observed.
In order to take into account these different thermal reaction characteristics of the turbine blade and surrounding housing and the demand for a small gap dimension between the blade tips and the housing, it is conventional that “contact” is allowed between the blade tips of the turbine blades and the surrounding housing. In order to prevent the blade tips of the turbine blades and the surrounding housing from being damaged in this case, a so-called abrasive coating is applied to the blade tips of the turbine blades, while the surrounding housing is coated with a corresponding wear or abrasion coating.
When the blade tip brushes against the abrasion coating introduced into the surrounding housing, the abrasive particles applied to the blade tip cut or rub into the abrasion coating and wear it away. At the same time, the abrasion of the abrasion coating is also associated with a certain amount of wear of the abrasive coating.
The wear of the abrasive coating applied to the blade tips of the turbine blades is a function of several factors, such as mating of material, temperature, rotational speeds, etc.
Rapid wear of the abrasive coating proves to be disadvantageous, since this leads, on one hand, to an increase in the gap between the blade tip and the surrounding housing, which, as described above, results in efficiency losses. On the other hand, the premature wear of the abrasive coating also means that the blade tips of the turbine blades are subject to premature wear themselves, i.e., practically ground down, which in turn leads to costly repairs of the blade tips and the shortening of the service life of the gas-turbine engine.
Using these findings as a starting point, it is an object of the present invention to provide corrective action, by redesigning the blade tips of a gas-turbine engine, in order to minimize the wear of the abrasive coating on-the blade tips, in particular in the region of the leading and trailing edges of the blade tips.